The invention concerns an interface circuit for actuating an electrical device, especially a pole-changing rotary-current induction motor, with a first contact element coordinated with a signal line carrying an alternating voltage signal in order to produce at least two control signals different from each other. The invention also concerns a circuit arrangement for actuating an electric motor, especially a pole-changing rotary-current induction motor, with a control-switching element having an aforesaid interface circuit, which is connected by a signal line to a control of the electric motor.
It is generally known how to transmit control signals between a control switch and an electric motor by a signal line. In this case, a control signal being transmitted is assigned to each wire of the line. The control signal is characterized by the presence of a voltage or the absence of a voltage on the signal line. One of these two signal states can then bring about functions such as “electric motor turns clockwise”.
In the case of the control of pole-changing rotary-current motors, the individual control signals in combination with each other bring about, for example, the functions: “slow left-hand rotation”, “slow right-hand rotation”, “fast left-hand rotation” and “fast right-hand rotation”. In this case, normally three control signals such as “right”, “left” and “fast” are produced by a control switch. If no voltage is present on the control line for the “fast” control signal, the rotary-current motor will turn slowly in the direction imposed by the other control signal. If several axes of a device are motorized with corresponding pole-changing rotary-current motors, additional control signals must be generated by the control switch corresponding to the number of axes. For a three-axis device, such as an industrial bay traveling crane, in which the lifting mechanism, the lifting mechanism trolleys, and the lifting beam are driven by pole-changing rotary-current motors, nine signals and thus also nine signal lines are required, in addition to a reference potential line. Thus, this system entails high costs and a large wiring expense on account of the large number of signal lines.
A customary method of reducing the necessary number of signal lines while maintaining the information content in the form of the different control signals is to convert the parallel signals into serial information. In the state of the art, many serial transmission types are known, from the RS232 interface familiar in PC equipment to bus systems which can very quickly and securely transmit the control signals. The converting of the parallel control signals into serial information and the converting of them back for the subsequent control process is, however, cost-intense. Also, a fault diagnosis for the serial transmission of control signals is more difficult than for parallel signal lines.